An electric power drive assembly is one of the core motive power assemblies of an electric vehicle or hybrid vehicle. Since the operating principle of an electric motor is different from that of an internal combustion engine, a high temperature will lead to an electric motor fault and thereby affect normal operation. An electric power drive assembly using an electric motor as a source of motive power is often provided with a cooling system for dissipating heat from the electric motor. This is commonly a liquid cooling system, i.e. a liquid coolant sleeve is provided outside the electric motor to enable liquid coolant to flow through regions from which heat needs to be dissipated, thereby lowering the temperature of the electric power drive assembly, and ensuring that the electric motor is within a reasonable operating temperature range.
The prior art is as shown in FIG. 1b. Due to the demands of installation and positioning, the liquid coolant sleeve outside the electric motor is often provided with multiple lugs for bolt fixing at an axial end thereof. In order to produce lugs at the end of the liquid coolant sleeve, it is necessary to use an annular blank with a larger original wall thickness. The wall thickness thereof must be greater than a radial dimension of the lugs, as shown in FIG. 1a. However, in order to produce lugs at just one end, most of the material of the annular blank will be removed during machining, to attain a liquid coolant sleeve wall thickness which meets requirements, therefore the degree of wastage of starting material is high. Moreover, due to the large area of machining, the process control requirements for machining are also high, and the processing procedure is complex, so processing costs are further increased.
At the same time, as shown in FIG. 2, since the liquid coolant sleeve is fixed to a housing directly using bolts, stress concentration points readily occur on the surfaces of contact of the liquid coolant sleeve and the housing due to insufficient matching, readily causing wear at contact positions and damage to components in the long term.
Hence, there is a need to provide a simpler production method having an improved durability and to produce an electric motor liquid coolant sleeve to solve the abovementioned problem.